The present invention is in the field of imaging systems. More particularly, the present invention provides a method and apparatus for ultrasonically applying a coating material onto a print substrate mounted on the plate cylinder of a printing press. In addition, the present invention provides a method and apparatus for ultrasonically cleaning the coating material from the surface of the print substrate prior to a reapplication of the coating material.
Lithography is the process of printing from specially prepared surfaces, some areas of which are capable of accepting lithographic ink, whereas other areas, when moistened by an aqueous dampening liquid, will not accept the ink. The image to be printed is provided on a lithographic printing master, such as a printing plate, which is mounted on the plate cylinder of a printing press. The printing master carries an image that is defined by the ink accepting areas of the printing surface. A print is obtained by applying ink and a dampening liquid to the printing surface and then transferring the ink from the ink accepting areas of the printing master, using a blanket cylinder, onto a substrate, typically formed of paper.
Many techniques have been used to form an image on a printing master. One common technique, often referred to as xe2x80x9ccomputer-to-film,xe2x80x9d transfers the image to be printed onto a supply of film using an imagesetter. After processing, the film is used as a mask for the imaging of a plate precursor, comprising, for example, a print substrate (e.g., an aluminum substrate) that has been coated with a thin layer of a photosensitive material. The imaged plate precursor is subsequently processed to obtain a printing plate that can be used as a printing master on a printing press.
Another technique, often called xe2x80x9ccomputer-to-platexe2x80x9d or xe2x80x9cdirect-to-plate,xe2x80x9d eliminates the need for film by transferring the image to be printed directly onto a plate precursor using a platesetter, an on-press imaging system, etc. The imaged plate precursor is then processed to obtain a printing plate that can be used as a printing master on a printing press. Upon completion of a press run, the printing master is removed from the plate cylinder of the printing press and discarded or recycled. A new printing master is then mounted onto the plate cylinder of the printing press in preparation of the next press run.
Recently, several computer-to-plate xe2x80x9con-pressxe2x80x9d imaging techniques have been developed that do not require the printing master to be removed from the plate cylinder of the printing plate upon completion of printing. For example, in one technique, a heat-sensitive coating material, capable of forming a lithographic printing form upon imaging and optional processing, is provided directly on the surface of a reusable hydrophilic print substrate mounted on the plate cylinder of the printing press. (Alternately, the coating material may be provided directly on the surface of the plate cylinder itself.) When the press run is complete, the reusable print substrate (or plate cylinder) is cleaned and recoated with the coating material, at which point it is ready for subsequent imaging and printing.
One such computer-to-plate technology, called LiteSpeed(trademark), recently developed by Agfa-Gevaert N.V. of Mortsel, Belgium, uses a polymer-type liquid lithographic coating material, designed to be sprayed or otherwise applied on an anodized aluminum print substrate, to create a lithographic printing form. The lithographic printing form can be imaged using thermal laser technology soon after application, and is then ready for printing. The non-exposed areas are removed from the lithographic printing form during the printing of the first few (e.g., 10) sheets of paper, allowing the press run to begin immediately after imaging without any additional development. At the end of the print run, the print substrate is completely cleaned prior to the next application of LiteSpeed(trademark) and the next concurrent print job. LiteSpeed(trademark) is non-ablative, requires no chemical processing, and each application is equal in performance to a conventional lithographic printing plate, with a run length of approximately 20,000 impressions.
On-press computer-to-plate systems, such as those described above, will require some form of cleaning prior to the reapplication of the coating material on the print substrate. LiteSpeed(trademark), and switchable polymer-type applied coating technologies, often require the removal of all of the applied polymer coating material, inks, and other contaminants prior to reapplication. The print substrate must be clean and dry prior to reapplication. One consequence of contamination is a latent or xe2x80x9cghost imagexe2x80x9d from the previous print run that may appear in the printed output of the next print run.
Many cleaning techniques have been proposed to clean a surface in a printing press. For example, U.S. Pat. No. 5,713,287 issued to Gelbart on Feb. 3, 1998 and U.S. Pat. No. 5,148,746 issued to Fuller et al. on Sep. 22, 1992, incorporated herein by reference, both describe cleaning devices and methods that use abrasive techniques to disengage materials from a surface. The former uses a cloth blanket type washer. The latter uses a type of brush or pad to dislodge materials, and a fan or other means for removal. The difficulty in these and other types of abrasive methods is the deteriorated surface condition left on the hydrophilic print substrate, and circumferential interruptions in the plate cylinder surface. These methods tend to produce a shorter print run length with less lithographic latitude. Some of the blanket washer types have the added disadvantage of requiring a full axial volume adjacent to the plate cylinder.
Another cleaning technique uses a stream of high pressure water to remove coating materials from the print substrate. After application of a cleaning solution, the stream of high pressure water is sprayed onto the print substrate. The water, removed coating material, inks, cleaner, and other contaminants are then removed from the print substrate using a vacuum system. The print substrate is then dried prior to the reapplication of the coating material. Great care must be taken when using this method to prevent the water and other substances removed from the print substrate from detrimentally affecting the on-press imaging system and other components/functions of the printing press. Subsequent filtration of large amounts of water having solubolized materials requires specialized equipment. As such, this process is difficult and costly to implement.
The coating material is commonly applied to the print substrate using a dedicated system that is independent from the cleaning and imaging systems. For example, the coating material may be applied to the print substrate by a spraying or a rolling system. Unfortunately, since access to the plate cylinder in the printing press is generally very limited, the implementation of separate coating, cleaning, and imaging systems is a complex and costly task.
Thus, there is a need for a method and apparatus for applying coating materials onto a print substrate, and for cleaning the coating materials from the print substrate, that avoids these and other problems present in currently available on-press systems.
The present invention provides methods and apparatus for applying a coating material onto, and cleaning the coating material from, a surface of a print substrate mounted on the plate cylinder of a printing press using ultrasonic techniques.
Generally, the present invention provides a method for applying a coating material onto a print substrate, comprising:
delivering a supply of the coating material to a distributive surface of an ultrasonic horn, the distributive surface controlling a flow of the coating material to an active edge of the ultrasonic horn, and atomizing the coating material at the active edge of the ultrasonic horn and directing the atomized coating material onto a surface of the print substrate.
The present invention also provides an apparatus for applying a coating material onto a print substrate, comprising:
an ultrasonic horn having a distributive surface and an active edge, and a delivery system for delivering a supply of the coating material to the distributive surface, the distributive surface controlling a flow of the coating material to the active edge, the active edge atomizing and directing the coating material onto the surface of the print substrate.
The present invention further provides an apparatus, comprising:
an ultrasonic horn having an active edge for atomizing and directing a coating material onto a print substrate, and a distributive surface for controlling a flow of the coating material to the active edge.